It is well known in the steel and iron industry that desulfurization or deoxidation of molten steel or iron may be accomplished by the addition of magnesium thereto. Various methods have been employed for introducing the magnesium into the molten iron or steel, e.g., adding Mg-containing pellets, powders, wires, rods, briquettes, etc. to the melt.
The present invention pertains to salt-coated magnesium particles for use in treating molten iron or steel and to a method for preparing the salt-coated magnesium particles.
It is well known that finely divided magnesium is easily oxidized and is subject to rapid combustion unless provided with a protective coating to guard against rapid oxidation.
It is believed that U.S. Pat. No. 3,881,913 and U.S. Pat. No. 3,969,104 (a divisional of U.S. Pat. No. 3,881,913) are illustrative of the most relevant prior art pertaining to the present invention. The patents teach the preparation of a magnesium-salt pellet by forming droplets of molten Mg in the presence of molten salt, then cooling the so-formed salt-coated Mg pellets. The patents also disclose that the Mg-salt pellets are useful for inoculating molten ferrous metals, e.g., for desulfurizing steel. U.S. Pat. No. 2,304,130; U.S. Pat. No. 2,699,576; U.S. Pat. No. 3,520,718; U.S. Pat. No. 2,676,359; and U.S. Pat. No. 2,934,789 are disclosed in U.S. Pat. No. 3,881,913 as being relevant art.
The present invention provides an alternate, improved method for producing salt-coated Mg pellets or granules and does not require that the salt or the Mg be molten during the salt-coating process. Furthermore, the present process provides a more uniform particle size and more consistent Mg/salt ratios than is provided by the use of the prior method of coating molten Mg beads with molten salt in a molten Mg bead generator.
It has long been known in the steel and iron industry that solid Mg cell sludge (which contains Mg, cell bath materials (salt), MgO and impurities) is marginally operable as an inoculant in ferrous melts when injected beneath the surface of the melt. Attempts have been made for many years to grind or pulverize the sludge to free the small beads of Mg which are dispersed in the sludge and then separate the beads from the friable, more powdery salts, leaving only a thin coating of the salts and impurities on the Mg beads. Such Mg beads, then, would ordinarily contain from about 40 to about 90% Mg.
The efficacy of such Mg beads retrieved from cell sludge as an inoculant for ferrous melts has been limited by the inconsistencies of the grinding and separation techniques and by the inconsistencies of the salt-coated Mg beads obtained therefrom. The steel and iron industries require relatively consistent batches of inoculants in order to avoid under-charging or over-charging the ferrous melts without having to adjust the injected amount according to varying pellet sizes and Mg concentrations.